Vacuum tube construction



Sept. 8, 1931.

F. S. M CULLOUGH VACUUM TUBE CONSTRUCTION Filed Dec. '7, 1921 LI, 1 a 1 2 ATTORNEY Freder/b/fi UNITED STATES PATENT A OFFICE FREDERICK S. MCCULLOUGH, OF-EDGEWOOD, PENNSYLVANIA, ASSIGNOB TO WESTING- HOUSE ELECTRIC & MANUFACTURING VANIA.

Application filed December whereby a high amplification factor may be obtained while simultaneously securing a comparatively low plate impedance.

In carrying my invention into effect, I provide an improved grid-filament structure, wherein a pair of controlling electrodes are provided, one of which extends concentrically to the axis of the enclosing envelope in the form of a conducting rod and the other of which is symmetrically disposed thereabout in the form of a helix. A filament is spirally wound around the conducting rod but insulated therefrom by a coating of dielectric material carried by the rod. An anode of cylindrical form surrounds the grid-filament structure, forming a space-current path between the filament and the anode.

Other objects and constructional details of my invention will be apparent from the following description and claims, when read in connection with the accompanying drawings, wherein Figure 1 is a front elevational view of a vacuum-tube device embodyin my invention, shown partly in section, and igure 2 is a detail view of Figure 1.

In the drawings, a vacuum-tube device 1 is shown in the form of an elongated tube 2 having an anode 3, a pair of co-operating controlling electrodes 4 and 5 and a filament 6 suitably disposed therein.

One of said pair of controlling electrodes is constructed in the form of a conducting rod 5, one end thereof being covered with an in- COMPANY, A CORPORATION OF PENNSYL- VACUUM TUBE CONSTRUCTION 7, 1921-. Serial No. 520,600.

sulating material 7, such, for example, as glass, quartz or fused enamel, and the other end extending through a press 8 to form a circuit connection 9.

The filamentary element 6 is shown in the form of a ribbon helically wound around the insulated portion 7 of the rod 5 and supported by conducting carrier rods 11 and 12 which are mounted'in the press 8. The ends of said rods may be extended through the press to form external circuit terminals 13 and 11 for the filament 6. The filament 6 may be formed of any material commonly used for such pur )oses. At present, I prefer to employ a ri bon of platinum iridium with a treatment of barium and strontium oxides so as to increase the rate of electron emission and permit the use of lower temperatures.

The other controlling electrode 4: is constructed in the form of a helical member and is so disposed as to completely surround the filament 6. The rod 5 and the electrode 4 are electrically united at their upper ends as shown at 19. Because the elements 4 and 5 together constitute the control electrode, the current through the junction 19 is never large. 1 Consequently, the effect of this connection is to maintain the elements 4 and 5 at substantially the same potential. The lower terminal of the helical member may be supported by a carrier rod 15 embedded in the press 8. Additional stifi'ness may be provided by extending the rod 15 along the outer cylindrical surfaceof the helix forming the grid 4 and welding said rod to several turns of the helix, as indicated at 10. The helical member 4 may be formed of any suitable material, such as tungsten, nickel, molybdenum etc.

The anode 3 is cylindrical in form and symmetrically disposed with respect to the previously mentioned elements. A carrier rod 16, which is mounted in the press 8, serves to support the anode 3 and may be extended through the press to form an external circuit terminal'17. The anode 3 may be formed of any suitable material commonly employed, such, for example, as nickel. or molybdenum.

In practice, I have obtained remarkably high amplification factors and low plate impedances. For example, with 80 volts impressed upon the plate anode, I have secured amplification factors ranging between 25 and 30 and plate impedances of approximately 30,000 ohms. The increase in the amplification factor is believed to be the result of the increase in the control of the electron emission afforded by the tube construction embodying my invention. The reduced plate impedance is believed to be caused by the increase in the active electron-emission surface provided, together with the greater permissible grid openings, while still retaining suitable control, and hence, amplification.

\Vhile I have shown only one embodiment of my invention in the accompanying drawings, it is capable of various changes and modifications Without departing from the spirit thereof and it is desired, therefore, that only such limitations shall be imposed thereon as are indicated in the prior art or in the appended claims.

I claim as my invention 1. A space-discharge device comprising a pair of concentrically disposed co-operating control elements and a fialmentary cathode entwined about the inner one only of said elements and subject to the electric field of both.

2. In a Vacuum-tube, a press, a conducting rod supported from said press, a helical member surrounding said rod at a distance therefrom and connected to said rod at the end away from the press, whereby the member is braced by the rod, said connection serving also to maintain said member and rod at the same potential, an anode and a cathode, the cathode being located in the electric field of both rod and member.

3. Ina vacuum tube, the combination with a press, of a conducting rod extending longitudinally therefrom, a filamentary cathode spirally Wound around said rod and insulatingly supported therefrom, a helical ele- 5. In a thermionic device, a central electrically conducting standard, a coating of refractory insulating material on said standard, a helical filament wound on said coating, lead wires from each end of said filament for supplying heating current thereto, a control electrode surrounding said filament and an anode surrounding said control electrode.

In testimony whereof, I have hereunto subscribed my name this 28th day of November, 1921.

FREDERICK S. MGCULLOUGH.

ment surrounding said rod and said cathode,

said helical element and said rod being electrically connected at the top and adapted to serve as a single control electrode, and a cylindrical anode surrounding said helical element.

4. In a vacuum tube device, a grid element, a cathode, a second grid element, and an anode, arranged to surround one another in the order named, a conductive connection between said grid elements, and an insulating body separating the inner grid element from thecathode and so arranged that the electron flow from said cathode is subjected to the controlling action of either grid. 

